A few months ago I switched my amd radeon rx390 with a powercolor rx7900xtx and I started to have some issues.
With my old gpu I never had any problems, but since installing my new one sometimes (not all the time) it seems to randomly shut down and restart my PC while playing certain games.
It seems to happen mostly with newer games and the older ones seem fine.
At first I thought it was the psu as the rx7900xtx has a minimum requirement of 800w on the psu, but mine should be enough as it should be able to draw 880w.
There is also no consistency as sometimes I can play a game for hours with no issues and other times it shuts down after a few minutes. Sometimes it shuts down just because I pressed the super key to look at the time.
It wouldn’t be so frustrating if I could check the logs, but journalctl doesn’t show anything.
I tried changing my settings in game to lower settings, updating my BIOS firmware and using the default settings, all without any luck.
The only thing I notice is that when I enable the MMIO to 4G and higher and enable the resize BAR, the shutdowns and restart increase by multitudes. Again only with the newer games.
Is there any way I can change the settings so the logs also register the random shutdowns and restarts? That way I can at least look at what causes these shutdowns?
The 7900XTX is power hungry - you should really recheck if your PSU can power the GPU.
I don’t know what it is - but if your
the shutdowns and restart increase by multitudes
then it is most likely the PSU - yes you say it should be adequate - perhaps that is correct on specifications - but the PSU has a lot of internal electronics - instead of a stable, flattened DC - it may be fluctuating - due to worn capacitors - I would look at replacing it with a new 1000w PSU.
The performance of psus lowers with time indeed. Always take one with enough buffer to account for aging. For real (on paper) need of 800w go with a 1000w so that even if after some years it only manages 900 you’d be safe.
From 800 to 880 is a bit on the edge.
If that’s the PSU’s rated capability, then there is not likely to be enough headroom left for the CPU, motherboard and storage devices, etc.; no wonder there’s an issue when the graphics card demands peak current.
… Although, I can’t imagine a graphics card ever needing anything like 800W on its own. You’d need some pretty hefty cooling. Maybe I’m just behind the times.
I’m seeing the same kind of intermittent shutdowns with no journalctl entry, and the fact that enabling ReBAR makes them happen more often is especially familiar. I’m also interested in a reliable way to capture the reset cause, since the usual logs stay empty.
ReBAR means Resizable BAR, a PCIe feature that lets the CPU access more of the GPU’s memory at once. Here it’s only a reported trigger for the resets, not a confirmed cause.
You’d need some pretty hefty cooling. 
Maybe I’m just behind the times. 